Scientific reticence and sea level rise
xnic...@hotmail.com
J E Hansen
NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY
10025, USA
E-mail: jha...@giss.nasa.gov
Submitted to Environmental Research Letters, March 23, 2007
Abstract
I suggest that a 'scientific reticence' is inhibiting communication of
a threat of potentially large sea level
rise. Delay is dangerous because of system inertias that could create
a situation with future sea level
changes out of our control. I argue for calling together a panel of
scientific leaders to hear evidence and
issue a prompt plain-written report on current understanding of the
sea level change issue.
(extract)
"The broader picture gives strong indication that ice sheets will, and
are already beginning to,
respond in a nonlinear fashion to global warming. There is enough
information now, in my opinion, to
make it a near certainty that IPCC BAU climate forcing scenarios would
lead to disastrous multi-meter
sea level rise on the century time scale.
There is, in my opinion, a huge gap between what is understood about
human-made global
warming and its consequences, and what is known by the people who most
need to know, the public and
policy makers. IPCC is doing a commendable job, but we need something
more. Given the reticence that
IPCC necessarily exhibits, there need to be supplementary mechanisms.
The onus, it seems to me, falls
on us scientists as a community."
Night of the Living Crackpots
Scientific reticence and sea level rise
J E Hansen
NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY
10025, USA
E-mail: jha...@giss.nasa.gov
Abstract I suggest that a `scientific reticence' is inhibiting
communication of a threat of potentially large sea level rise. Delay
is dangerous because of system inertias that could create a situation
with future sea level changes out of our control. I argue for calling
together a panel of scientific leaders to hear evidence and issue a
prompt plain-written report on current understanding of the sea level
change issue.
Keywords Sea level, global warming, glaciology, ice sheets
Subject classification (PACS) 92.05.Df -- Climate and inter-annual
variability 92.40.Vq -- Glaciology 92.70.Mn -- Impacts of global
change; global warming 92.70.Jw -- Oceans, sea level
Submitted to Environmental Research Letters, March 23, 2007
1. Introduction
I suggest that `scientific reticence', in some cases, hinders
communication with the public about dangers of global warming. If I am
right, it is important that policy-makers recognize the potential
influence of this phenomenon.
Scientific reticence may be a consequence of the scientific method.
Success in science depends on objective skepticism. Caution, if not
reticence, has its merits. However, in a case such as ice sheet
instability and sea level rise, there is a danger in excessive
caution. We may rue reticence, if it serves to lock in future
disasters.
Barber (1961) describes a `resistance by scientists to scientific
discovery', with a scholarly discussion of several sources of cultural
resistance. There are aspects of the phenomenon that Barber discusses
in the `scientific reticence' that I describe, but additional factors
come into play in the case of global climate change and sea level
rise.
I can illustrate `scientific reticence' best via personal experiences.
The examples are relevant to the Intergovernmental Panel on Climate
Change (IPCC) process of consensus building, specifically to the issue
of possible sea level rise.
2. The Court Case.
`Scientific reticence' leapt to mind as I was being questioned, and
boxed-in, by a lawyer for the plaintiff in Automobile Manufacturers
versus California Air Resources Board (Auto Manufacturers 2006). I
conceded that I was not a glaciologist. The lawyer then, with aplomb,
requested that I identify glaciologists who agreed publicly with my
assertion that sea level was likely to rise more than one meter this
century if greenhouse gas emissions followed an IPCC business-as-usual
(BAU) scenario: "Name one!"
I could not, instantly. I was dismayed, because, in conversation and e-
mail exchange with relevant scientists I sensed a deep concern about
likely consequences of BAU global warming for ice sheet stability.
What would be the legal standing of such a lame response as
`scientific reticence'? Why would scientists be reticent to express
concerns about something so important? I suspect the existence of what
I call the "John Mercer effect". Mercer (1978) suggested that global
warming from burning of fossil fuels could lead to disastrous
disintegration of the West Antarctic ice sheet, with sea level rise of
several meters worldwide. This was during the era when global warming
was beginning to get attention from the United States Department of
Energy and other science agencies. I noticed that scientists who
disputed Mercer, suggesting that his paper was alarmist, were treated
as being more authoritative.
It was not obvious who was right on the science, but it seemed to me,
and I believe to most scientists, that the scientists preaching
caution and downplaying the dangers of climate change fared better in
receipt of research funding. Drawing attention to the dangers of
global warming may or may not have helped increase funding for
relevant scientific areas, but it surely did not help individuals like
Mercer who stuck their heads out. I could vouch for that from my own
experience. After I published a paper (Hansen et al 1981) that
described likely climate effects of fossil fuel use, the Department of
Energy reversed a decision to fund our research, specifically
highlighting and criticizing aspects of that paper at a workshop in
Coolfont, West Virginia and in publication (MacCracken 1983).
I believe there is a pressure on scientists to be conservative. Papers
are accepted for publication more readily if they do not push too far
and are larded with caveats. Caveats are essential to science, being
born in skepticism, which is essential to the process of investigation
and verification. But there is a question of degree. A tendency for
`gradualism' as new evidence comes to light may be ill-suited for
communication, when an issue with short time fuse is concerned.
However, these matters are subjective. I could not see how to prove
the existence of a `scientific reticence' about ice sheets and sea
level. Score one for the plaintiff, and their ally and `friend of the
court', the United States federal government.
Night of the Living Crackpots
3. On the Ice
A field glaciologist, referring to a moulin on Greenland, said: "the
whole damned ice sheet is going to go down that hole!" He was talking
about his expectations, under the assumption of continued unchecked
growth of global GHG emissions. Field glaciologists have been doing a
good job of reporting current trends on the ice sheets. It is
translation of field data into conclusions needed by the public and
policymakers that is at issue.
Ice sheet disintegration, unlike ice sheet growth, is a wet process
that can proceed rapidly. Multiple positive feedbacks accelerate the
process once it is underway. These feedbacks occur on and under the
ice sheets and in the nearby oceans.
A key feedback on the ice sheets is the `albedo flip' (Hansen et al
2007) that occurs when snow and ice begin to melt. Snow-covered ice
reflects back to space most of the sunlight striking it. However, as
warming causes melting on the surface, the darker wet ice absorbs much
more solar energy. Most of resulting melt water burrows through the
ice sheet, lubricates its base, and thus speeds discharge of icebergs
to the ocean (Zwally et al. 2002).
The area with summer melt on Greenland increased from ~450,000 km2
when satellite observations began in 1979 to more than 600,000 km2 in
2002 (Steffen et al 2004). Linear fit to data for 1992-2005 yields an
increase of melt area of +40,000 km2 per year (Tedesco 2007), but this
rate may be exaggerated by the effect of stratospheric aerosols from
the 1991 volcanic eruption of Mount Pinatubo, which reduced summer
melt in 1992. Summer melt on West Antarctica has received less
attention than on Greenland, but it is more important. Satellite
QuickSCAT radiometer observations reveal increasing areas of summer
melt on West Antarctica and an increasing melt season length during
the period 1999- 2005 (Nghiem et al 2007).
The key role of the ocean, in the matter of ice sheet stability, is as
a conduit for excess global- scale heating that eventually leads to
melting of ice. The process begins with increasing human-made
greenhouse gases, which cause the atmosphere to be more opaque at
infrared wavelengths. The increased atmospheric opacity causes heat
radiation to space to emerge from a higher level, where it is colder,
thus decreasing radiation of heat to space. As a result, the Earth is
now out of energy balance by between 0.5 and 1 W/m2 (Hansen et al
2005).
This planetary energy imbalance is itself now sufficient to melt ice
corresponding to one meter of sea level rise per decade, if the energy
were used entirely for that purpose (Hansen et al 2005). However, so
far most of the excess energy has been going into the ocean.
Acceleration of ice sheet disintegration requires tapping into ocean
heat, which occurs primarily in two ways (Hansen 2005): (1) increased
velocity of outlet glaciers (flowing in rock-walled channels) ice
streams (bordered mainly by slower moving ice), and thus increased
flux and subsequent melting of icebergs discharged to the open ocean,
and (2) direct contact of ocean and ice sheet (underneath and against
fringing ice shelves). Ice loss from the second process has a positive
feedback on the first process: as buttressing ice shelves melt, ice
stream velocity increases.
Positive feedback from loss of buttressing ice shelves is relevant to
some Greenland ice streams, but the West Antarctic ice sheet, which
rests on bedrock well below sea level (Thomas et al 2004), will be
affected much more. Loss of ice shelves provides exit routes with
reduced resistance for ice from further inland, as suggested by Mercer
(1978) and earlier by Hughes (1972). Warming ocean waters are now
thinning some West Antarctic ice shelves by several meters per year
(Payne et al 2004; Shepherd et al 2004).
The Antarctic Peninsula recently provided a laboratory to study
feedback interactions, albeit for ice volumes less than those in the
major ice sheets. Combined actions of surface melt (van den Broeke
2005) and ice shelf thinning from below (Shepherd et al 2003) led to
sudden collapse of the Larsen B ice shelf, which was followed by
acceleration of glacial tributaries far inland (Rignot et al 2004;
Scambos et al. 2004). The summer warming and melt that preceded ice
shelf collapse (Fahnestock et al. 2002; Vaughan et al 2003) was no
more than the global warming expected this century under BAU
scenarios, and only a fraction of expected West Antarctic warming with
realistic polar amplification of global warming.
Modeling studies yield increased ocean heat uptake around West
Antarctica and Greenland due to increasing human-made greenhouse gases
(Hansen et al 2006b). Observations show a warming ocean around West
Antarctica (Shepherd et al 2004), ice shelves thinning several meters
per year (Rignot and Jacobs 2002; Payne et al 2004), and increased
iceberg discharge (Thomas et al 2004). As discharge of ice increases
from a disintegrating ice sheet, as occurs with all deglaciations,
regional cooling by the icebergs is significant, providing a temporary
negative feedback (Hansen 2005). However, this cooling effect is
limited on global scale as shown by comparison with the planetary
energy imbalance, which is sufficient to melt ice equivalent to about
one meter of sea level per decade (Table S1 of Hansen et al. 2005).
Indeed, cooling of the ocean surface by melting ice increases the
planetary energy imbalance, thus supplying additional energy for ice
melt, so the planetary energy imbalance should not be thought of as a
limit on the rate of ice melt.
Global warming should also increase snowfall accumulation rates in ice
sheet interiors because of the higher moisture content of the warming
atmosphere. Despite high variability on interannual and decadal time
scales, and limited Antarctic warming to date, observations tend to
support this expectation for both Greenland and Antarctica (Rignot and
Thomas 2002; Johannessen et al 2005; Davis et al 2005; Monaghan et al
2006). Indeed, some models (Wild et al 2003) have ice sheets growing
overall with global warming, but those models do not include realistic
processes of ice sheet disintegration. Extensive paleoclimate data
confirm the common sense expectation that the net effect is for ice
sheets to shrink as the world warms.
The most compelling data for the net change of ice sheets is provided
by the gravity satellite mission GRACE, which shows that both
Greenland (Chen et al 2006) and Antarctica (Velicogna et al 2006) are
losing mass at substantial rates. The most recent analyses of the
satellite data (S. Klosco et al priv. comm.) confirm that Greenland
and Antarctica are each losing mass at a rate of about 150 cubic
kilometers per year, with the Antarctic mass loss primarily in West
Antarctica. These rates of mass loss are at least a doubling of rates
of several years earlier, and only a decade earlier these ice sheets
were much closer to mass balance (Casenave 2006).
The Antarctic data are the most disconcerting. Warming there has been
limited in recent decades, at least in part due to effects of ozone
depletion (Shindell and Schmidt 2004). The fact that West Antarctica
is losing mass at a significant rate suggests that the thinning ice
shelves are already beginning to have an effect on ice discharge
rates. Warming of the ocean surface around Antarctica (Hansen et al
2006a) is small compared with the rest of world, consistent with
climate model simulations (IPCC 2007), but that limited warming is
expected to increase (Hansen et al 2006b). The detection of recent,
increasing summer surface melt on West Antarctica (Nghiem et al 2007)
raises the danger that feedbacks among these processes could lead to
nonlinear growth of ice discharge from Antarctica.
Night of the Living Crackpots
4. Urgency:
This Problem is Non-Linear! IPCC business-as-usual (BAU) scenarios
are constructs in which it is assumed that emissions of CO2 and other
greenhouse gases will continue to increase year after year. Some
energy analysts take it as almost a law of physics that such growth of
emissions will continue in the future. Clearly, there is not
sufficiently widespread appreciation of the implications of putting
back into the air a large fraction of the carbon stored in the ground
over epochs of geologic time. Climate forcing due to these greenhouse
gases would dwarf the climate forcing for any time in the past several
hundred thousand years, when accurate records of atmospheric
composition are available from ice cores.
However, the long-term global cooling and increase of global ice
through the Plio-Pleistocene provides an even more poignant
illustration of the implications of continued BAU burning of fossil
fuels. The global oxygen isotope record of benthic (deep ocean
dwelling) foraminifera compiled by Lisieki and Raymo (2005), repeated
in Figure 10a of Hansen et al (2007) for comparison with solar
insolation changes over the same period, reveals long-term cooling and
sea level fall, with superposed oscillations at a dominant frequency
of 41 ky. The long-term cooling presumably is due, at least in part,
to drawdown of atmospheric CO2 by weathering that accompanied and
followed the rapid growth of the Andes (Ghosh et al 2006), which was
most rapid in the late Miocene. Changes in meridional heat transport
may have contributed to the climate trend (Rind and Chandler 1991),
but the CO2 amount providing a global positive forcing seems unlikely
to have been more than approximately 350-450 ppm (Dowsett et al 1994;
Raymo et al 1996; Crowley 1996). Global mean temperature three million
years ago was only 2-3°C warmer than today (Crowley 1996; Dowsett et
al 1996), while sea level was 25 ± 10 m higher (Wardlaw and Quinn
1991; Barrett et al 1992; Dowsett et al 1994).
The Plio-Pleistocene record compiled by Lisieki and Raymo (2005) is
fascinating to paleoclimatolgists as it clearly shows the expected
dominance of global climate variations with the 41 ky cyclic variation
of the tilt of the Earth's spin axis, increased tilt melting ice at
both poles. When the planetary cooling reached a degree that allowed a
large mid-latitude Northern Hemisphere (Laurentide) ice sheet, the
periodicity necessarily became more complex, because of the absence of
land area for a similar ice sheet in the Southern Hemisphere (Hansen
et al 2007). However, the information of practical importance from the
Plio-Pleistocene record is the implication of dramatic global climate
change with only moderate global climate forcing. With global warming
of only 2-3°C and CO2 of perhaps 350-450 ppm it was a dramatically
different planet, without Arctic sea ice in the warm seasons and sea
level 25 ± 10 m higher.
Assuming a nominal `Charney' climate sensitivity of 3°C equilibrium
global warming for doubled CO2 , BAU scenarios yield a global warming
at least of the order of 3°C by the end of this century. However, the
Charney sensitivity is the equilibrium (long-term) global response
when only fast feedback processes (changes of sea ice, clouds, water
vapor and aerosols in response to climate change) are included (Hansen
et al 2007). Actual global warming would be larger as slow feedbacks
come into play. Slow feedbacks include increased vegetation at high
latitudes, ice sheet shrinkage, and terrestrial and marine greenhouse
gas emissions in response to global warming.
In assessing likely effects of warming of 3°C, it is useful to note
the effects of the 0.7°C warming in the past century (Hansen et al
2006a). This warming already produces large areas of summer melt on
Greenland and significant melt on West Antarctica. Global warming of
several more degrees, with its polar amplification, would have both
Greenland and West Antarctica bathed in summer melt for extended melt
seasons.
The IPCC (2007) midrange projection for sea level rise this century is
20-43 cm [8-17 inches] and its full range is 18-59 cm [7-23 inches].
IPCC notes that they are unable to evaluate possible dynamical
responses of the ice sheets, and thus do not include any possible
"rapid dynamical changes in ice flow". Yet the provision of such
specific numbers for sea level rise encourages a predictable public
response that projected sea level change is moderate, and indeed
smaller than in IPCC (2001). Indeed, there have been numerous media
reports of "reduced" sea level rise predictions, and commentators have
denigrated suggestions that business-as-usual greenhouse gas emissions
may cause sea level rise measured in meters. However, if these IPCC
numbers are taken as predictions of actual sea level rise, as they
have been by the public, they imply that the ice sheets can
miraculously survive a BAU climate forcing assault for a period of the
order of a millennium or longer. This is not entirely a figment of the
IPCC decision to provide specific numbers for only a portion of the
problem, while demurring from any quantitative statement about the
most important (dynamical) portion of the problem. Undoubtedly there
are glaciologists who anticipate such long response times, because
their existing ice sheet models have been designed to match
paleoclimate changes, which occur on millennial time scales.
However, Hansen et al (2007) show that the typical ~6ky time scale for
paleoclimate ice sheet disintegration reflects the half-width of the
shortest of the weak orbital forcings that drive the climate change,
not an inherent time scale of ice sheets for disintegration. Indeed,
the paleoclimate record contains numerous examples of ice sheets
yielding sea level rise of several meters per century, with forcings
smaller than that of the BAU scenario. The problem with the
paleoclimate ice sheet models is that they do not generally contain
the physics of ice streams, effects of surface melt descending through
crevasses and lubricating basal flow, or realistic interactions with
the ocean.
Rahmstorf (2007) has noted that if one uses observed sea level rise of
the past century to calibrate a linear projection of future sea level,
BAU warming will lead to sea level rise of the order of one meter in
the present century. This is a useful observation, as it indicates
that sea level change would be substantial even without non-linear
collapse of an ice sheet. However, this approach cannot be taken as a
realistic way of projecting likely sea level rise under BAU forcing.
The linear approximation fits the past sea level change well for the
past century only because the two terms contributing significantly to
sea level rise were (1) thermal expansion of ocean water and (2)
melting of alpine glaciers.
Under BAU forcing in the 21st century, sea level rise undoubtedly will
be dominated by a third term (3) ice sheet disintegration. This third
term was small until the past few years, but it is has at least
doubled in the past decade and is now close to 1 mm/year, based on
gravity satellite measurements discussed above. As a quantitative
example, let us say that the ice sheet contribution is 1 cm for the
decade 2005-2015 and that it doubles each decade until the West
Antarctic ice sheet is largely depleted. That time constant yields sea
level rise of the order of 5 m this century. Of course I can not prove
that my choice of a 10 year doubling time for non-linear response is
accurate, but I am confident that it provides a far better estimate
than a linear response for the ice sheet component of sea level rise.
An important point is that the non-linear response could easily run
out of control, because of positive feedbacks and system inertias.
Ocean warming and thus melting of ice shelves will continue after
growth of the forcing stops, because the ocean response time is long
and the temperature at depth is far from equilibrium for current
forcing. Ice sheets also have inertia and are far from equilibrium:
and as ice sheets disintegrate their surface moves lower, where it is
warmer, subjecting the ice to additional melt. There is also inertia
in energy systems: even if it is decided that changes must be made, it
may require decades to replace infrastructure.
The nonlinearity of the ice sheet problem makes it impossible to
accurately predict sea level change on a specific date. However, as a
physicist, I find it almost inconceivable that BAU climate change
would not yield a sea level change measured in meters on the century
time scale. The threat of large sea level change is a principal
element in our argument (Hansen et al 2006a,b, 2007) that the global
community must aim to keep additional global warming less than 1°C
above 2000 temperature. In turn, this implies a CO2 limit of about 450
ppm, or less. Such scenarios are dramatically different than BAU,
requiring almost immediate changes to get on a fundamentally different
energy and greenhouse gas emissions path.
Night of the Living Crackpots
5. Reticence
Is my perspective on this problem really so different than that of
other members of the relevant scientific community? Based on
interactions with others, I conclude that there is not such a great
gap between my position and that of most, or at least much, of the
relevant community. The apparent difference may be partly a natural
reticence to speak out, which I attempt to illuminate via specific
examples.
In the late 1980s Richard Kerr wrote an article titled "Hansen vs. the
World on the Greenhouse Threat", reporting on a scientific conference
in Amherst, Massachusetts. One may have surmised strong disagreement
with my assertion (to Congress) that the world had entered a period of
strong warming due to human-made greenhouse gases. But participants
told Kerr "if there were a secret ballot at this meeting on the
question, most people would say the greenhouse warming is probably
there." And "what bothers us is that we have a scientist telling
congress things that we are reluctant to say ourselves."
That article made me notice right away a difference between scientists
and `normal people'. A non-scientist friend from my hometown, who had
congratulated me after my congressional testimony, felt bad after he
saw the article by Kerr. He obviously believed that I had been shown
to be wrong. However, I thought Kerr did a good job of describing the
various perspectives, and made it clear, at least between the lines,
that differences were as much about reticence to speak as about
scientific interpretations. IPCC reports may contain a reticence in
the sense of being extremely careful about making attributions. This
characteristic is appropriately recognized as an asset that makes IPCC
conclusions authoritative and widely accepted. It is probably a
necessary characteristic, given that the IPCC document is produced as
a consensus among most nations in the world and represents the views
of thousands of scientists.
Kerr (2007) describes a specific relevant example, whether IPCC should
include estimates of dynamical ice sheet loss in their projections:
"too poorly understood, IPCC authors said", and "overly cautious
(dynamical effects) could raise sea level much faster than IPCC was
predicting" some scientists responded. Kerr goes on to say "almost
immediately, new findings have emerged to support IPCC's conservative
position." Glaciologist Richard Alley, an IPCC lead author, said "Lots
of people were saying we [IPCC authors] should extrapolate into the
future, but we dug our heels in at the IPCC and said that we don't
know enough to give an answer."
6. Our Legacy
Reticence is fine for IPCC. And individual scientists can choose to
stay within a comfort zone, not needing to worry that they say
something that proves to be slightly wrong. But perhaps we should also
consider our legacy from a broader perspective. Do we not know enough
to say more?
Confidence in a scientific inference can be built from many factors.
For climate change these include knowledge gained from studying
paleoclimate changes, analysis of how the Earth has responded to
forcings on various time scales, climate simulations and tests of
these against observations, detailed study of climate change in recent
decades and how the nature of observed change compares with
expectations, measurements of changes in atmospheric composition and
calculation of implied climate forcings, analysis of ways in which
climate response varies among different forcings, quantitative data on
different feedback processes and how these compare with expectations,
and so on.
Can the broader perspective drawn from various sources of information
allow us to `see the forest for the trees', to `separate the wheat
from the chaff'? That a glacier on Greenland slowed after speeding up,
used as `proof' that reticence is appropriate, is little different
than the common misconception that a cold weather snap disproves
global warming. Spatial and temporal fluctuations are normal, short-
term expectations for Greenland glaciers are different from long-term
expectations for West Antarctica.
Integration via the gravity satellite measurements puts individual
glacier fluctuations in proper perspective. The broader picture gives
strong indication that ice sheets will, and are already beginning to,
respond in a nonlinear fashion to global warming. There is enough
information now, in my opinion, to make it a near certainty that IPCC
BAU climate forcing scenarios would lead to disastrous multi-meter sea
level rise on the century time scale.
There is, in my opinion, a huge gap between what is understood about
human-made global warming and its consequences, and what is known by
the people who most need to know, the public and policy makers. IPCC
is doing a commendable job, but we need something more. Given the
reticence that IPCC necessarily exhibits, there need to be
supplementary mechanisms. The onus, it seems to me, falls on us
scientists as a community.
Important decisions are being made now and in the near future. An
example is the large number of new efforts to make liquid fuels from
coal, and a resurgence of plans for energy intensive "cooking" of tar-
shale mountains to squeeze out liquid hydrocarbon fuels. These are
just the sort of actions needed to preserve a BAU greenhouse gas path
indefinitely. We know enough about the carbon cycle to say that at
least of the order of a quarter of the CO2 emitted in burning fossil
fuels under a BAU scenario will stay in the air "forever", the latter
defined practically as more than 500 years. Readily available
conventional oil and gas are enough to take atmospheric CO2 to a level
of the order of 450 ppm.
In this circumstance it seems vital that we provide the best
information we can about the threat to the great ice sheets posed by
human-made climate change. This information, and necessary caveats,
should be provided publicly, and in plain language. The best
suggestion I can think of is for the National Academy of Sciences to
carry out a study, in the tradition of the Charney and Cicerone
reports on global warming. I would be glad to hear alternative
suggestions.
Acknowledgments I thank Tad Anderson, Mark Bowen, Svend Brandt-
Erichsen, Jost Heintzenberg, John Holdren, Ines Horovitz, Bruce
Johansen, Ralph Keeling, John Lyman, Maureen Raymo, Christopher
Shuman, Richard Somerville, and Bob Thomas for comments on a draft
version of this paper.
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xnic...@hotmail.com
>
> Johannessen O M, Khvorostovsky K, Miles M W, Bobylev L P 2005 Recent
> ice-sheet growth in the interior of Greenland Science 310 1013-6
>
> Kerr R A 1989 Hansen vs. the world on the greenhouse threat Science
> 244 1041-3 Kerr R A 2007 Predicting fate of glaciers proves slippery
>
> Lisiecki L E and Raymo M E 2005 A Pliocene-Pleistocene stack of 57
> globally distributed benthic 18O records Paleoceanogr. 20 PA1003 doi:
> 10.1029/2004PA001071
>
> MacCracken, M C 1983 Climatic effects of atmospheric carbon dioxide
> Science 220 873-4 Mercer J 1978 West Antarctic ice sheet and CO2
> greenhouse effect: a threat of disaster Nature 271 321-5
>
> Monaghan A J et al 2006 Insignificant change in Antarctic snowfall
> since the International Geophysical Year Science 313 827-31
>
>
> read more »
Read and digest: there will be a test later.....